All Weapons & Full Ammo
start a new game and at during the first cutscene type A-X-X-Y-B-X-A-A that should make you invincible and give you max ammo and weaponry that's the real insane cheat.
[Warning! Not Verified]

Hint: Defeating The Boss
In order to fight the Boss, you have to eliminate all of the hitmen. This will make the Boss battle much easier. When you have killed all of the hitmen, enter the confession room on the left. This is the one that you pray in during the first level's loading screen. The priest will be in the confession room directly next to you, being held captive by the Russian general. The only way to get the general out is to crouch down and shoot a bullet at the heart on the confession booth's inside wall. A short intermission will start and the general will come out, firing an SP12. Use any automatic rifle and fire, making sure every bullet connects. Make sure you have the full amount of ammunition equipped in the gun. He should die within a few seconds.

Hint: Gun Collection
Throughout all the levels you will run into many different types of guns. Whenever you see a gun that you do not already have, pick it up. After you complete the level on which you found the gun, the gun will now be available at your house. You will have ammunition in the room for you to use if desired. However, there are many guns that are too big to carry inside your clothes and therefore must be held in the open. You will not be able to pick up a gun of the same size or greater without dropping the one you are holding. You will find other guns on the same level that you cannot pick up because you are already holding one, and the gun you want is simply too big to conceal. In this case, you will have to decide which gun you want more then finish the level with it. You can always replay that level to get the other gun that was left behind.